The Effect of Ionizing Radiations on the Broad Bean Root, Part X

Abstract

Experiments and observations which suggest that the sensitivity of tumour and normal tissues to X rays is affected by the oxygen supply are described in the literature from an early date. In particular, Crabtree and Cramer (1933) showed that anærobiosis decreased the sensitivity of tumour tissue irradiated in vitro by X rays, and Mottram (1935), stimulated by their experiment, obtained a similar result on the broad bean root (Vicia faba) both with X and γ radiation. Gray (1942) suggested that the lethal effect of ionizing radiations on the growing tip of the Vicia faba root resulted from the production of chromosome aberrations. If this were correct, then fewer aberrations should be produced by irradiation in the absence of oxygen than by the same dose when oxygen was present. This was tested by Thoday and Read (1947), who found that the proportion of anaphases which showed bridges and fragments was about three times larger when roots were irradiated in water containing 18 c.c. oxygen per litre, compared with the proportion when the same dose was given to the roots in oxygen-free water. As a by-product of this experiment the growth curves of groups of bean roots shown in Fig. 1 were obtained. Each curve shows the averaged growths of 9 roots: Nos. 1, 2, and 3 representing those irradiated anærobically, and 4, 5, and 6 those in water containing 6 c.c. oxygen per litre.